Take a look at several of the many mystery writer organizations that give annual awards in the mystery genre. The Shamus , Agatha, Edgar, Anthony, MacAvity, and Barry awards are all listed on the BookReporter.com website's award section as well as having their own websites. The Mystery Writers of America website lists the Edgars and other MWA awards. The awards are divided up into best first mystery, best paperback original, lifetime achievement, best non-fiction, best short story, and so on. The Shamus award is for books with a P.I. protagonist (Private Investigator.) The Agathas celebrate the mystery in the traditional style of Agatha Christie. Each organization explains its criteria and specialty on its website.
I can't list a favorite for 2005, but I just finished Death Without a Trace by Gerard Murphy about Irish brewer, Madigan, of Dublin who works as an investigator on the side to earn money to pay child support/alimony to his ex-wife. The novel takes the form of a "noir" mystery; Madigan has a rather dismal existence and takes a dim view of life in modern Ireland. Look on Amazon's United Kingdom site for more information on this book and other books from the U.K.